Many mammals, including humans, exhibit reflexive testosterone release during sexual encounters. However, the function of this release is unclear. This proposal is based upon the hypothesis that reflexive testosterone release has immediate effects upon the male's physiology and behavior to better prepare him to cope with the reproductive situation in which he finds himself. Scattered supportive evidence in the scientific literature indicates that testosterone treatment in rodents has quick effects in promoting male sexual reflexes and is experienced by male rodents as being rewarding, anxiolytic, and analgesic, all of which could potentially facilitate the expression of reproductive behavior. The proposed studies will test that hypothesis more explicitly by examining whether several different endpoints (reward and anxiety) in normal male mice are affected by the quick actions of testosterone when it is administered in such a way as to mimic naturally occurring testosterone release. Several questions will be addressed including 1) How does one best mimic the pulsatile testosterone release of gonadally intact males? 2) Is the reflexive release of testosterone experienced as rewarding in mice? 3) What level of sexual arousal is necessary before a male muse shows reflexive testosterone release? 4) Does the reflexive release of testosterone exert different effects upon physiology and behavior than spontaneous testosterone release in mice? The proposed research is basic research designed to better understand the role that reflexive testosterone release plays in normal male-typical behaviors. However, since reflexive testosterone release is evolutionarily conserved, we believe our results also will have relevance for understanding the same processes in other mammalian species including humans. Moreover, we believe that our results may also be directly relevant for understanding the seemingly addictive (i.e., rewarding) properties of anabolic steroid use in humans as well. [unreadable] [unreadable]